Characterization and molecular identification of Phytophthora spp. associated with Phytophthora blight of vegetables in Texas. R.D. French-Monar 1 , Z. G. Abad 2 , A. F. Patton III 1 , and T. Isakeit 3 1 Dept. of Plant Pathology, AgriLife Extension-Texas A&M, Amarillo, TX, USA. 2 USDA-APHIS-PPQ-PSPI Molecular Diagnostics Lab., Beltsville, MD, USA. 3 Dept. of Plant Pathology , Texas A&M University, College Station, TX, USA.
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Characterization and molecular identification of Phytophthora spp.
associated with Phytophthorablight of vegetables in Texas.
R.D. French-Monar1, Z. G. Abad2, A. F. Patton III1 , and T. Isakeit3
1Dept. of Plant Pathology, AgriLife Extension-Texas A&M, Amarillo, TX, USA. 2USDA-APHIS-PPQ-PSPI Molecular Diagnostics Lab., Beltsville, MD, USA.3Dept. of Plant Pathology , Texas A&M University, College Station, TX, USA.
Texas High Plains Plant Diagnostic Laboratory
Texas AgriLife Research and Extension Center6500 Amarillo Blvd. WAmarillo, Texas 79106
TEXAS RAINFALL: GO EAST, GET WET
Texas = 2.25X Size of Italy
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Phytophthora blightυ Caused by Phytophthora capsici (oomycete)
υ Devastating on pepper, cucurbits, tomato, and eggplant
υ Spread by surface water, wind and splashing rains.
υ Present in Texas for over 60 years.
Symptoms
P. capsici in Texas High Plainsυ 2006: First known report on pumpkin and
winter squash (Isakeit, 2007): 36 acres – 2% field affected August; 78% lost next month– Yoakum County
υ 2007:10-12 acres of chile pepper in a 60 acre field affected by this pathogen.– Gaines County
Morphological
υ These isolates had semi-papillate to papillatesporangia, caducous sporangia with pedicels that exceeded 35 μm in length.
υ Sporangia 37 to 40 X 21 to 23 μmυ Exhibited heterothallism; no chlamydospores. υ When paired with an opposite mating type,
oospores produced were mostly aplerotic.υ Oogonia were amphigynous in their antheridial
attachment.υ Oospores 25 to 27 μm in diameter.
French-Monar et al. 2006. Plant Dis. 90: 345-350
Isakeit, T. 2007. Plant Dis. 91: 633
Phytophthora capsici from Capsicum annuum
Photos by Gloria Abad, Ph.D USDA/APHIS/MDL 8.18.08
2007 Field (Yoakum County): No Phytophthora blight
2007 Field (Gaines County)
Phytophthora blight on peppers Ronald French
(Texas A&M-TCE)
Phytophthora blight on bell pepper
Phytophthora blight in Texas
Chile pepper
Phytophthora sp. on watermelon
Texas
Compatibility type determination
υ For compatibility type determination:– a 6-mm mycelial plug of a known A1 or A2 mating type
is added to one side of a clarified V8 juice agar plate.– on the opposite side, the isolate of unknown mating type
is added to the agar plate.– After 7 days, the center of the plate is observed under
Methodology (cont.)υ For mefenoxam sensitivity studies:
– 10% clarified V8 juice agar was amended with 0, 5, and 100 µg/ml of mefenoxam (Ridomil Gold EC).
– A plug of mycelium is set at the center of each plate.– After three days, colony diameters are measured at each
concentration.– Growth of >40% of control at 100 µg/ml= Resistant– Growth of >40% of control at 5 µg/ml = Intermediate– Growth of <40% of control= Sensitive.
Neighbor joining phylogenetic tree with 1000 bs based on the ITS1-5.8S-ITS2 complete region of Phytophthora Clade 2 (Cooke et al 2000) showing the position of samples from vegetables in Texas to representative sequences of P. capsici and other known taxa in the clade. Pythium vexans is outgroup. Scale bar unit: number of nucleotide substitutions per site.
CL2
Phy. sp. caroliniana Ph268.99.6102 from strawberry NC- Homothallica
υ How can the pathogen survive and persist in the Texas High Plains?
Common Purslane (Portulaca oleracea)
Andy Bennett
French-Monar et al. 2006. Plant Dis. 90:345-350.
Carolina Wild Geranium (Geranium carolinianum)
Daniela Bell
French-Monar et al. 2006. Plant Dis. 90:345-350.
Nightshades (Solanum spp.)
http://www.agf.gov.bc.ca French-Monar et al. 2006. Plant Dis. 90:345-350.
Conclusionsυ Phytophthora blight devastation in Texas may not
be solely the responsibility of P. capsiciυ Up to 4 species of Phytophthora might be involved
in Phytophthora blight of vegetables.υ Isolates from watermelon (2008, S. Texas), winter
squash (2006, N. Texas) and chile pepper (collection, S. Texas) had a perfect alignment for P. capsici.
Conclusionsυ Isolates from chile pepper in N. Texas perfectly
aligned with P. mexicana.υ The pumpkin isolate (N. Texas) did not group with
any Phytophthora sp. and could represent a new species.
υ Chile pepper isolate from S. Texas did not grouped with another isolate from chile pepper (Mexico) and closely related to a species to be reported by G. Abad on strawberry.